1. Field of the Invention
The present invention generally relates to an optical pickup, which can record and reproduce the information recorded at high density in correspondence with an information record medium capable of high density recording such as a so-called DVD or the like, and an information recording and reproducing apparatus using the optical pickup.
2. Description of the Related Art
In case of recording and reproducing the information by use of a light beam such as a laser light or the like with respect to the information record medium on which the information is recorded, the light beam is condensed or focused onto an information record surface of the information record medium by use of an objective lens.
In this case, as the smaller is the size of a light spot which is formed on the information record surface by the irradiation of the light beam, the higher is the density of recording and reproducing the information. The size (i.e. the diameter) of the light spot is expressed by .lambda./NA, wherein NA represents a numerical aperture of the objective lens, and .lambda. represents a wavelength of the light beam. Thus, as the larger is the numerical aperture NA of the objective lens, it is possible to reduce the size of the light spot.
However, if the numerical aperture NA is increased too much, from the relationship with the thickness of the information record medium, the tilt at the time of recording and reproducing, or the focal depth of the light beam, the tolerable range of the thickness, tilt or focal depth decreases to exceed the servo control capability. Therefore, the practical numerical aperture NA at the present is set to be the value about 0.6.
Consequently, as a technique to improve the numerical aperture NA while maintaining the tolerable range of the thickness of the information record medium etc., a technique to insert a so-called immersion lens between the objective lens and the information record surface is presently developed, as disclosed in Applied Physics letter, Vol.57, No.57, No24, Dec. 10, 1990, pp 2515 to 2516, for example. The immersion lens is constructed such that a half sphere shaped small lens (which is called as an immersion lens) is disposed between the objective lens and the information record surface in such a state that a flat portion thereof is objected to the information record surface, so as to improve the numerical aperture NA by means of the refraction of the light beam by the immersion lens. More concretely, the immersion lens increases an incident angle .theta. of the light beam onto the information record surface by the refraction, so that the numerical aperture NA proportional to the sine .theta. is increased, without the necessity of increasing the size or thickness of the objective lens or the number of the objective lenses.
The optical pickup including the above mentioned immersion lens is provided with a support member, which supports the immersion lens and maintains the positional relationship between the immersion lens and the information record surface. Then the information record medium is not rotated, the support member contacts with the information record medium. When the information record medium is rotated, a thin layer of air is formed between the information record medium and the support member, so that the support member is spaced from the information record medium.
However, assuming that the information record medium is an optical disc for example, if the optical disc is rotated, at the initial period of the rotation, the external surface of the transparent protection layer of the optical disc is scratched by the support member, which results in a problem that the light beam is unintentionally refracted or attenuated by the scratch, and the record and reproduction of the information cannot be normally performed.